A transmission, such as an automatic transmission, includes a case, which houses an oil pump. The oil pump supplies hydraulic oil through an oil passage to an oil pressure control mechanism in the case. One type of such an oil pump is driven by torque received from a shaft (input shaft), which is located in a torque input route extending from the engine to the transmission. Another type of such an oil pump is driven and rotated by a shaft that is separate from and rotated in cooperation with the input shaft. Japanese Laid-Open Patent Publication Nos. 2003-301929 and 2007-198418 describe such a separate shaft type oil pump.
To avoid enlargement of the transmission case, the separate shaft type oil pump may be arranged in an area below a section between the input shaft and output shaft of the transmission. However, a manual shaft such as a parking control shaft may also be arranged in such an area. When the oil pump and the manual shaft are arranged in the same area, the transmission case must be enlarged downward so that the oil pump and the manual shaft do not interfere with each other. This increases the weight of the transmission and decreases the ground clearance of the transmission when installed in a vehicle.
To solve this problem, Japanese Laid-Open Patent Publication No. 2007-198418 inserts the manual shaft through a hole formed in a support wall, which supports the oil pump. A plate is arranged between the oil pump and the support wall so that an oil passage of the oil pump does not interfere with the hole of the support wall. A groove is formed in the surface of the plate. An oil passage connecting the oil pressure control mechanism and the oil pump is formed by guiding oil with the groove to a position at which interference does not occur.
Thus, the support wall, which is arranged in the case, must have a sufficient thickness to allow for the insertion of the manual shaft. Further, the plate must have a sufficient area to allow for the formation of the interference-prevention groove in its surface. Accordingly, the weight of the transmission case cannot be effectively decreased.